1. Field of Invention
This invention relates to a vibration control device, a stage device, and an exposure apparatus, and more specifically to a vibration control device which holds an object and controls vibration, a stage device provided with the vibration control device, and an exposure apparatus having the stage device.
2. Description of Related Art
Conventionally, in a lithographic process which manufactures a semiconductor element, a liquid crystal display element, or the like, it is known to use a step-and-repeat type reduction projection exposure apparatus (so-called stepper) or a step-and-scan type scanning projection exposure apparatus (so called scanning stepper). The stepper transfers a pattern formed in a mask or a reticle (hereafter referred to as “reticle”) onto a substrate such as a wafer, a glass plate, or the like coated by a resist or the like via a projection optical system while the reticle and substrate are stationary. The scanning stepper improves upon the stepper in that it synchronously moves the reticle and substrate during exposure, thereby increasing the imaging field.
In these types of exposure apparatus, a positional relationship among a projection optical system, a wafer, and a reticle is most important, and is the main factor which determines exposure performance capability. Because of this, the positional relationship among a projection optical system, a reticle stage on which a reticle is mounted, and a wafer stage on which a wafer is mounted is measured by an optical position sensor (e.g., an interferometer, a synchronizing detecting wave type optical system, or the like), and positioning between the reticle and the wafer is performed with high accuracy based on the measurement result.
In order to accomplish the positioning with high accuracy, it is desirable to isolate vibrations from being transmitted to the projection optical system, the wafer stage, and the reticle stage from sources of vibrations. Examples of vibration factors (vibration sources) are: (a) external vibration (micro vibration) of a clean room floor surface (i.e., the foundation or supporting surface of the machine) in which an exposure apparatus is installed; (b) so-called called return vibration in which, when a reaction force that accompanies the driving of the stage and that is generated within the exposure apparatus is transmitted to the floor, particularly when the floor rigidity is weak, the reaction force oscillates the floor surface and the vibration returns to the exposure apparatus from the floor surface and becomes a vibration factor of the exposure apparatus; (c) vibration in which a reaction force generated at the time of the driving of the reticle stage or the wafer stage oscillates a supporting plate in which guide surfaces of the stages are formed, and this vibration is transmitted to the projection optical system via a body of the exposure apparatus; and (d) vibration from a cable, a wiring, conduits or the like connected to the stages.
In the exposure apparatus, in order to control or prevent the various vibrations from being transmitted to the projection optical system, the wafer stage, the reticle stage, and other parts of the body of the exposure apparatus are supported by a vibration control mechanism. With respect to the vibration control mechanism, there are many mechanisms that support a target object (i.e., the stages, etc.) by three or four points. For example, in the case of a vibration control mechanism supporting the exposure apparatus itself, it is desirable that a vibration control effect is seen relative to six degrees-of-freedom directions (X, Y, Z, θz, θx, θy) with respect to the floor. This is because if the floor or the apparatus itself is considered as an elastic body instead of a rigid body, even if a vibration occurs in a specified direction, depending on the oscillating mode, there is a possibility that the vibration can be converted to various vibration directions.
FIG. 17(A) schematically shows an example of a conventional vibration control device. A vibration control device 931 shown in FIG. 17(A) is provided with an air cushion portion 951 supporting a support target object OB and a micro driving portion 976 which can micro-drive the support target object OB in a gravity direction (vertical direction within a paper plane of FIG. 17(A)) with high responsiveness.
The air cushion portion 951 is provided with a housing 961 having an upper aperture, a holding member 962 which is provided on an elastic member that seals the aperture of the housing 961 and holds the support target object OB, a diaphragm 963 (the elastic member) which connects the holding member 962 with the housing 961, and, along with the housing 961 and the holding member 962, forms a gas chamber 969 in a substantially air tight state, and an electromagnetic regulator 955 which adjusts gas, e.g., air pressure, filled within the gas chamber 969.
Furthermore, the micro driving portion 976 is provided with a voice coil motor 974 having movable portions 974a directly fixed to the support target object OB and stators 974b which electromagnetically interact with the movable portions 974a and generate an electromagnetic force which drives the support target object OB in a gravity direction, and an electric current supply source 975 which supplies a driving electric current to the voice coil motor 974.
In the vibration control device 931 thus structured, for example, if an offset load is generated along with the movement of the stage arranged on the support target object OB, according to the output of an undepicted displacement sensor (e.g., an optical position sensor or the like), based on the measurement value of an undepicted pressure sensor, the electromagnetic regulator 955 is controlled, and gas within the gas chamber 969, e.g., an air pressure is controlled. However, the internal pressure of the gas within the gas chamber is high, so only approximately 20 Hz of control response is obtained. Therefore, if a high response control is needed, according to the output of an undepicted accelerometer or the like, the voice coil motor 974 needs to be controlled. Of course, micro vibration, such as floor vibration is removed by an air spring of the air cushion portion 951.
In FIG. 17(B), a vibration control device 931′ is shown in which a metal bellows forming an internal gas chamber is used for an air cushion portion 951′. Even in the case of using this type of structure, if the structure is relatively light, in the same manner as the vibration control device of FIG. 17(A), vibration control and movement of the support target object OB is effectively performed.